1. Field of the Invention
The present invention relates to a configuration for preventing a waveform of an optical signal from degrading in an optical exchanger (cross-connect node).
2. Description of the Related Art
As information is being exchanged at high speed and in large volumes, a demand for networks and transmission systems with a broad band and large capacity has increased. As one means for meeting this demand the construction of an optical network is desired. An optical transmission system is a key factor in the construction of an optical network, and there is a wavelength-multiplexed optical cross-connect (XC) system as one system for such an optical transmission network. A wavelength-multiplexed optical XC refers to a photonic switching system of wavelength-multiplexed optical signals.
FIG. 1 shows the configuration of a wavelength-multiplexed optical XC and an optical network using the wavelength-multiplexed optical XC.
In the diagram the optical network comprises optical amplifiers 1500-1 through 1500-4 and optical transmission line 1501-1 through 1501-4 for connecting these optical amplifiers. A wavelength-multiplexed optical XC 1502 accommodates a plurality of optical input/output transmission line, and routes wavelength-multiplexed optical signals inputted from input optical transmission line to the desired output optical transmission line for each wavelength. The routing is controlled by an operating system 1503 provided in another network controller (not shown in the diagram). The operating system 1503 controls switching in the wavelength-multiplexed optical XC 1502, and monitors from which transmission line optical signals are inputted and to which transmission line optical signals are outputted to.
It is desirable from the viewpoint of miniaturized hardware that the configuration of the wavelength-multiplexed optical XC 1502 can be implemented without converting optical signals to electrical signals. However, as transmission distance and the number of passed nodes increase, noise generated by the optical amplifiers (spontaneous emission light) and crosstalk from other channels are accumulated, and thereby the waveforms of optical signals are degraded (that is, the error rate characteristic is degraded).
There are two systems in a wavelength-multiplexed optical XC system; that is, one is a system in which the wavelength is not converted in the node (fixed wavelength type) and the other is a system in which the wavelength is converted, if necessary (converted wavelength type).
FIGS. 2A and 2B, respectively, show the general configurations of fixed and converted wavelength type wavelength-multiplexed optical XCs using an optical switch.
The fixed wavelength type shown in FIG. 2A comprises a demultiplexer 1600, a wavelength-corresponding optical switch (optical SW) unit 1601, a multiplexer 1603 and a regenerator 1602 (consisting of an electrical/optical converter and an optical/electrical converter), and routes an input optical signal to the desired output transmission line with the wavelength unchanged by controlling the optical switch unit 1601. On the other hand, the converted wavelength type shown in FIG. 2B uses an optical switch unit 1604 with such a capacity that the same number of optical signals as the product of the number of wavelengths n multiplied by a port number k can be accommodated, and the optical switch unit 1604 is controlled so that the wavelength of an optical signal can be converted to the desired wavelength of the desired output transmission line.
FIGS. 3A and 3B, respectively, show the general configurations of fixed and converted wavelength type wavelength-multiplexed optical XCs using a wavelength filter.
The fixed wavelength type shown in FIG. 3A comprises a wavelength selector unit 1700, a demultiplexer 1701, a multiplexer 1703 and a regenerator 1702, and the wavelength selector 1700 controls using a wavelength selection filter, etc. so that optical signals of the same wavelength may not be outputted to the same output. On the other hand, the converted wavelength type shown in FIG. 3B uses a wavelength selector unit 1704 with such a capacity that the wavelength-multiplexed optical signals and the same number of optical signals as the product of the number of wavelengths n multiplied by a port number k can be accommodated for the input and output, respectively, and the wavelength selector unit 1704 is controlled so that the wavelength of an optical signal can be converted to the desired wavelength of the desired output transmission line.
As described above, the regenerators in the converted wavelength types shown in FIGS. 2B and 3B are used to convert a wavelength in addition to the regeneration function.
In the conventional configurations, although a regenerator is used, the noise and crosstalk generated in an optical XC node are combined with the noise and crosstalk generated in the transmission line. Accordingly, the error rate characteristic is degraded.
Therefore, it is necessary to prevent the noise and crosstalk generated in the optical XC node from mixing with the noise and crosstalk generated in the transmission line or to suppress the noise and crosstalk themselves in order to solve the conventional problems.
It is an object of the present invention to provide an optical XC node with a configuration for suppressing the noise and crosstalk generated in the transmission line and the noise and crosstalk generated in an optical XC node, and thereby suppressing the degradation of the error rate characteristic.
The optical exchanger of the present invention is a photonic switching apparatus for accommodating a plurality of wavelength-multiplexed optical input/output optical links, routing wavelength-multiplexed optical signals inputted from each input link, and outputting the optical signals to output links, and is characterized in comprising a demultiplexer for demultiplexing wavelength-multiplexed optical signals inputted from the input link to optical signals of each wavelength, a first regenerator for regenerating the optical signals of each wavelength outputted from the demultiplexer and compensating for the S/N ratio degradation due to propagation in the transmission line, an optical switch unit for receiving the optical signals outputted from the first regenerator, and routing and outputting the optical signals, a second regenerator for regenerating the optical signals outputted from the optical switch unit and compensating for the S/N ratio degradation generated in the optical exchanger, and a multiplexer for multiplexing the optical signals of each wavelength outputted from the second regenerator to wavelength-multiplexed optical signals and outputting the wavelength-multiplexed optical signals to the transmission line.
The optical exchanger in another aspect of the present invention is a photonic switching apparatus for accommodating a plurality of wavelength-multiplexed optical input/output optical links, routing wavelength-multiplexed optical signals inputted from each input link, and outputting the optical signals to output links, and is characterized in comprising a first demultiplexer for demultiplexing wavelength-multiplexed optical signals inputted from the input link to optical signals of each wavelength, a first regenerator for regenerating the optical signals of each wavelength outputted from the demultiplexer and compensating for the S/N ratio degradation due to propagation in the transmission line, a first multiplexer for multiplexing the optical signals of each wavelength outputted from the first regenerator, a wavelength selector unit, consisting of two optical couplers and one multi-wavelength selection filter for routing the wavelength-multiplexed optical signals from the first multiplexer, a second demultiplexer for demultiplexing the optical signals outputted from the wavelength selector unit to optical signals of each wavelength, a second regenerator for regenerating the optical signals of each wavelength from outputted from the second demultiplexer and compensating for the S/N ratio degradation generated in an optical exchanger, and a second multiplexer for multiplexing the optical signals outputted from the second regenerator and outputting the wavelength-multiplexed optical signals to the transmission line.
The optical exchanger in another aspect of the present invention is a photonic switching apparatus for accommodating a plurality of wavelength-multiplexed optical input/output optical links, routing wavelength-multiplexed optical signals inputted from each input link, and outputting the optical signals to output links, and is characterized in comprising a demultiplexer for demultiplexing wavelength-multiplexed optical signals inputted from the input link to optical signals. of each wavelength, a first regenerator for regenerating the optical signals of each wavelength outputted from the demultiplexer and compensating for the S/N ratio degradation due to propagation in the transmission line, a first multiplexer for multiplexing the optical signals of each wavelength outputted from the first regenerator, a wavelength selector unit, consisting of two optical couplers and one wavelength selection filter for routing the wavelength-multiplexed optical signals inputted from the first multiplexer, a second regenerator for regenerating optical signals from the optical signals of each wavelength outputted from the wavelength selector unit and compensating for the S/N ratio degradation generated in an optical XC node, and a second multiplexer for multiplexing the optical signals of each wavelength outputted from the second regenerator and transmitting then to the transmission line.
According to the present invention, by providing a regenerator for optical signals on the input side of an optical exchanger and eliminating noise and crosstalk degrading the S/N ratio of optical signals prior to routing, only the compensation for the S/N ratio degradation due to the noise generated by optical amplifiers provided in the optical exchanger and the crosstalk due to routing, is needed in a regenerating means provided on the output side of the optical exchanger. That is, since the regeneration means on the input side of the optical exchanger compensates for the S/N ratio degradation due to the transmission line beforehand, and the error rate characteristic in the case where optical signals are regenerated on the output side is improved. Accordingly, the error rate characteristic of the entire optical exchanger is also improved.